Unmanned air vehicles (UAVs) are becoming increasingly prevalent and the performance requirements desired of UAVs are similarly increasing. In this regard, it is desired that UAVs have a long range and high endurance in order to carry out operations far from their base. Additionally, it is desirable for some UAVs to be capable of being launched from and recovered off of relatively small ships. Still further, it is desirable for the speed of UAVs to be increased while the signature of the UAVs is decreased such that UAVs become more survivable.
While UAVs that are capable of a conventional take-off and landing have been developed, some applications demand a vertical take-off and landing capability, such as those applications in which the UAV is to be launched from a relatively small ship. One type of UAV that is capable of vertical take-off and landing is a ducted fan, tail-sitting UAV, also known as Coléoptéres with one example being shown in FIG. 1. The ducted fan UAV 10 includes a central pod 12 that houses an engine. The engine, in turn, drives a propeller 14 for propulsion and vertical lift, such as during vertical take-off and landing. The propeller is housed within a shroud 16 that augments the thrust for take-off. Additionally, the ducted fan UAV includes one or more vanes 18 in the exhaust flow to control the vehicle in pitch, yaw and roll. In operation, the ducted fan UAV is capable of vertical take-off. Following take-off, the ducted fan UAV can transition to forward flight during which the shroud serves as a ring wing. In order to extend the wing span to provide for a longer range, the ducted fan UAV may also include wing extensions 20 extending radially outward from opposed sides of the shroud.
The ducted fan UAV 10 of FIG. 1 has a relatively high speed in comparison to a helicopter of comparable size. However, the ducted fan UAV is not particularly survivable and generally has a larger radar cross section and acoustic signature than desired. In addition, the range of the ducted fan UAV is inferior to a fixed wing UAV as a result of its relatively short wing span. In this regard, the relatively short span of the duct translates into greater drag and correspondingly shorter range in comparison to a comparable fixed wing UAV that is designed for a more conventional take-off and landing. The range and signature of the ducted fan UAV is also impaired by the inclusion of substantial control electronics as are required to provide three-axis control of the ducted fan UAV while in a hovering position.
Accordingly, while UAVs and, more particularly, UAVs capable vertical take-off and landing have been developed, it would be desirable to increase the range and the endurance of these UAVs to permit operation of the UAVs in theaters further removed from their base. Additionally, it would be desirable to develop UAVs, such as UAVs capable of vertical take-off and landing, that can be launched from and recovered off of relatively small ships so as to increase the scenarios in which the UAVs can be deployed.